True air speed indicator

ABSTRACT

An air speed indicator has a pointer movable over a fixed scale to display the indicated air speed of the aircraft. A rotatable dial having a true air speed scale thereon is co-axial with the fixed dial and visible therethrough. The rotatable dial is connected through gearing and linkage to an ambient density sensor which is responsive to ambient temperature and altitude pressure. The sensor means comprises a single system including a gas filled bulb responsive to ambient temperature connected to a diaphram in the instrument case, the case being subjected to altitude pressure.

United States Patent Mollick Aug. 29, 1972 [54] TRUE AIR SPEED INDICATOR3,126,737 3/1964 Gibbs ..73/181 Inventor: Milm lli ll Pa. Homs X [7 3]Assignee: Ametek, Inc., New York, N.Y. primary 1 i 22 Filed: May 6, 1970Attorney-5mm & Moore [21] Appl. No.2 35,210 57 ABSTRACT An air speedindicator has a pointer movable over a (g1 ..73/ fi scale to display theindicaed air speed of the I! c craft. A rotatable i l having a true iSpeed Scale [58] Fleld of Search ..73/182, 393, 368.7, 181, 183 thereonis coaxial with the fixed dial and visible therethrough. The rotatabledial is connected through [56] References C'ted gearing and linkage toan ambient density sensor UNITED STATES PATENTS which is responsive toambient temperature and altitude pressure. The sensor means comprises asingle ystem including a gas responsive to an 3,340,731 9/1967 Hunter..73/ 182 biem temperature connected to a diaphram in the fi l strumentcase, the case being subjected to altitude aw 1,633,380 6/1927 Irwin..73/393 X pressure 2,662,757 12/1953 Mock ..73/368.7 X 6 Claims, 7Drawing Figures Til P- SENSOR Patented Aug. 29, 1972 3,686,944

3 Sheets-Sheet l I v smlc PRESSURE 1o IIIS'I'.CA$E TUBE TEMP. SENSORFIG.2A

INVE 10 /Lnw LL/CK TTORNEYS Patented Aug. 29, 1972 3 Sheets-Sheet 2 T0PITOT TUBE (RAM PRESSURE) My LL/ 6/( who MM ATTORNEY$ B To PITOT TUBE(STATIC PRESSURE.)

Patented Aug. 29, 1972 3,686,944

3 Sheets-Sheet 5 lNVEN OR ,kkyjn W 0.4M 64' ATTORNEYS TRUE AIR SPEEDINDICATOR The present invention relates to an air speed indicator foraircraft wherein both the indicated air speed and true air speed will besimultaneously indicated. Indicated air speed in present instruments isa function of the pressure difference between the total and staticpressure as obtained from the pitot tube. In order to obtain the trueair speed of the aircraft or vehicle relative to the atmosphere in whichit is located, a density correction must-be made, the correctiondepending upon the ambient temperature and the altitude pressure.

Air speed indicators are known which indicate simultaneously the trueand indicated air speed. However, such instruments are undulycomplicated in that they employ a separate pointer for each air speed,or use a number of sensors to measure temperature and pressure.

One of the objects of the present invention is to provide an improvedand simple air speed indicator for indicating simultaneously the trueand indicated air speed of an aircraft.

In one aspect of the present invention, an air speed indicator foraircraft may comprise a fixed dial having an indicated air speed scalethereon. A rotatable dial is positioned concentrically with the fixeddial and has a true air speed scale thereon. The fixed dial may betransparent so that the rotatable dial is visible therethrough. Apointer is mounted for rotary move ment about an axis co-axial with thedial for indicating simultaneously an aligned set of scaled markings onboth dials. Operatively connected to the pointer is a means responsiveto the differential air pressure from the pitot tube for moving thepointer over the dials to show the indicated air speed. Operativelyconnected to the rotatable dial is single density sensor meansresponsive to both the ambient temperature and/or and pressure altitudefor moving the dial so that the true air speed will be indicated by thepointer when the pointer is positioned in response to an indicated airspeed.

The single sensor means preferably comprises a gas filled bulb vwhich isexposed to the atmosphere surrounding the aircraft. The air speedindicator is enclosed in a sealed casing to retain ambient staticatmospheric pressure therein.

Other objects, advantages and features of the present invention willbecome apparent from the following description and drawings, which aremerely exemplary.

In the drawings:

FIG. 1 is a view of the dial faces of the indicator according to thepresent invention showing the graduated scales thereon;

FIG. 2 is a schematic representation showing the operative connectionbetween the pointer and the pitot tube for indicating indicated airspeed;

FIG. 2A is a schematic representation showing the connection between thetemperature and altitude pressure sensor and a rotatable dial forindicating true air speed;

FIG. 3 is a front view of the instrument according to the presentinvention with the dial faces cutaway;

FIG. 4 is an elevational or side view looking in the direction of thearrows 4-4 of FIG. 3;

FIG. 5 is an enlarged elevational or side view looking in the directionof the arrows 5-5 of FIG. 3; and

FIG. 6 is a reduced size elevational or side view of the instrumentcasing assembly with a portion of the casing being cut away.

Proceeding next to the drawings wherein like reference symbols, whereappropriate, indicate the same parts throughout the various views, aspecific embodiment of the present invention will be described indetail.

With particular reference to FIGS. 3-6, an air speed indicator accordingto the present invention is indicated generally at 10 in FIG. 6 whichcomprises a sealed casing 1 1, which may be of plastic, with an open end11A covered by a transparent window of glass or plastic 12 (FIG. 3) heldin position by ring 13.

Dial 14 is secured by screws 15 (FIG. 4) to mounting posts 16. Aroundthe outer periphery of dial 14 is the indicated air speed scale 17 (FIG.1). Pointer 18 is movable relative to dial 14 and is mounted onrotatable shaft 19 which is concentric with dial 14. Near the lower endof shaft 19 (FIG. 4) is a pinion gear 20 meshing with sector gear 21pivotally mounted at 22. Tubular or arbor shaft element 23 is concentricwith sector gear axis 22 and is secured to gear 21. Extending radiallyoutwardly from arbor shaft element 23 is pin 24 which is engaged byanother pin 25 extending upwardly from rocker arm 26 joumal led betweenpointed pivot means 27. Rocker arm 26 has a second pin 28 extendingtherefrom engagable by pin 29 secured to movable part of diaphragm 30.As schematically shown in FIG. 2, the altitude static pressure isconducted by tube 30A to the interior of the sealed instrument casing.The interior of diaphragm 30 is connected to the pitot tube totalpressure connection 30B through connection 31. The diaphragm 30 istherefore responsive to the difference between total and staticpressure. Movement of diaphragm 30 will move pointer 18 to show theaircraft indicated air speed.

The true air speed is indicated on rotatable dial 32 (FIG. 4) which isco-axial with dial l4 and pointer 18 and has pinion gear 33A secured toits underside. Dial 32 has a graduated scale 33 thereon to indicate trueair speed. Dial 32 is positioned immediately below dial 14 and isvisible therethrough. Instead of making dial 14 transparent, thestationary dial may be provided with a slotted portion 19A through whichthe scale markings on rotatable dial 32 are visible. Also, the dials canbe made so that the true air speed dial indications are at the rim ofthe indicated air speed dial and the indicated air speed is on a centraldial.

Dial 32 is rotated by means of a sector gear 34 (FIGS. 3, 5) pivoted at35 and having pin 36 extending radially therefrom. Pin 36 is engaged bypin 37 extending from rocker arm 38 journalled on pointed bearings 39.Extending outwardly from rod 38 is a pin 40 engagable by a second pin 41extending from the movable side of diaphragm 42 which is responsive topressure altitude and temperature.

To sense the temperature of the ambient atmosphere, a gas filled bulb 43(FIG. 2A) is connected in series with diaphragm 42 through flexible tube44. Bulb 43 and diaphragm 42 are filled with an inert gas which ismaintained at a predetermined pressure and temperature at time offilling. The volume of bulb 43 is relatively large with respect to thevolume of diaphragm 42 so that only variations of the bulb temperaturewill cause temperature corrections. The diaphragm will respond toambient static pressure variations because it is enclosed in the sealedinstrument casing which is subject to static altitude pressure.

Since the bulb 43 and flexible tube 44 are rigid as com pared to thediaphragm, the bulb and tube will not respond to static pressurevariations. With this construction, the movement of the rotatable dial32 will represent a correction factor as imposed by ambient temperatureand altitude pressure which is a function of the density of the airthrough which the airplane is flying.

It will be understood that various details of construction andarrangement of parts may be made without departing from the spirit ofthe invention except as defined in the appended claims.

What is claimed is:

1. In an air speed indicator for aircraft, a fixed'dial having anindicated air speed scale thereon, a rotatable dial concentric with saidfixed dial and having a true air speed scale thereon visible inconjunction with said indicated air speed scale, a pointer mounted forrotary movement about an axis co-axial with said dials for indicatingsimultaneously an aligned set of scale rotatable dial for moving saiddial, said bulb being predeteminedly filled to combine pressure andtemperature response to provide the density correction so that the trueair speed will be indicated by the pointer when the pointer ispositioned in response to the indicated air speed.

2. In an air speed indicator as claimed in claim 1 wherein at said fixeddial is transparent, said rotary dial being mounted below said fixeddial.

3. In an air speed indicator as claimed in claim 1 wherein said gascomprises an inert gas at a pressure equal to or less than atmosphericpressure.

4. In an air speed indicator as claimed in claim 1 wherein the pressureof the inert gas in the diaphragm and bulb combination may bepreadjusted to provide an optimum density correction, the volume of thebulb being relatively large with respect to the volume of the diaphragm.v

5. In an air speed indicator as claimed in claim 1 and comprising apinion gear co-axially mounted on said rotary dial, a sector gearmeshing with said pinion gear, and linkage means between said diaphragmand sector gear for transmitting the movement of the diaphragm to saidrotatable dial through said sector and pinion gears.

6. In an air speed indicator as claimed in claim 1 and comprising asealed casing enclosing theair speed indicator and to retain staticatmospheric pressure.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa Q 86,944A1JgusL29 l91P Inventor (5) Milton MOlliCk It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1, line 36, "and/or" should be deleted. Column L, line after "at"insert --least a portion of".

Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETC HER JR. ROBERT GOTTSCHA LK Attesting Officer Commissionerof Patents FORM USCOMM-DC scan-poo U 5. GOVERNMENT PRINTING OFFICE I 90-15-33,

1. In an air speed indicator for aircraft, a fixed dial having anindicated air speed scale thereon, a rotatable dial concentric with saidfixed dial and having a true air speed scale thereon visible inconjunction with said indicated air speed scale, a pointer mounted forrotary movement about an axis co-axial with said dials for indicatingsimultaneously an aligned set of scale markings on both dials, meansresponsive to differential air pressure and operatively connected tosaid pointer for moving said pointer over the dials to indicate theindicated air speed, and single density sensor means responsive to theambient atmospheric temperature and the ambient static altitude pressurecomprising a diaphragm connected in series with a gas filled bulbexposed to the surrounding atmosphere, said single sensor means beingoperatively connected to said rotatable dial for moving said dial, saidbulb being predeterminedly filled to combine pressure and temperatureresponse to provide the density correction so that the true air speedwill be indicated by the pointer when the pointer is positioned inresponse to the indicated air speed.
 2. In an air speed indicator asclaimed in claim 1 wherein at said fixed dial is transparent, saidrotary dial being mounted below said fixed dial.
 3. In an air speedindicator as claimed in claim 1 wherein said gas comprises an inert gasat a pressure equal to or less than atmospheric pressure.
 4. In an airspeed indicator as claimed in claim 1 wherein the pressure of the inertgas in the diaphragm and bulb combination may be preadjusted to providean optimum density correction, the volume of the bulb being relativelylarge with respect to the volume of the diaphragm.
 5. In an air speedindicator as claimed in claim 1 and comprising a pinion gear co-axiallymounted on said rotary dial, a sector gear meshing with said piniongear, and linkage means between said diaphragm and sector gear fortransmitting the movement of the diaphragm to said rotatable dialthrough said sector and pinion gears.
 6. In an air speed indicator asclaimed in claim 1 and comprising a sealed casing enclosing the airspeed indicator and to retain static atmospheric pressure.